Most current motor vehicles include a front bumper system intended to resist and/or absorb impact loads in the event of a collision. Typically, the bumper system includes a rigid bumper beam extending transversely relative to the vehicle and having sufficient strength to resist a required level of impact energy. The bumper beam is mounted to and supported by the vehicle frame, sub-frame, and/or body structure. In some cases, the bumper beam is mounted to the forward ends of a pair of frame rails which extend longitudinally relative to the vehicle and are spaced apart transversely. Often, the forward-most portion of the forward frame, immediately behind the bumper beam, comprises crush cans which are engineered to deform or collapse longitudinally in a manner to absorb impact energy in a predictable manner. The bumper system may also include numerous other bumper members and/or trim members connected to the bumper beam and/or the forward frame members. Bumper systems may also include one or more fascia components exposed over and covering the bumper.
Several current national and multi-national vehicle safety regulatory bodies have formulated pedestrian safety standards which new vehicles will be measured against. At least one such pedestrian safety test attempts to measure or estimate the degree of injury that will be inflicted on the lower leg of standing or walking pedestrian if struck by a relatively slow-moving vehicle. These tests generally indicate that a greater vertical distance between the bumper and the road surface may result in greater injury to the pedestrian's lower leg, because the lower leg may slide underneath the bumper.
Simply lowering the height of the bumper in order to improve performance in such a test may not be a practical solution because of the resulting reduction in vehicle ground clearance. Having a relatively large ground clearance is particularly important for vehicles that must operate off of paved surfaces.
It is known to provide a so-called lower leg stiffener below the bumper which is intended to prevent the bumper from over-riding the pedestrian's lower leg, and therefore reduce the likelihood and/or the severity of injury during a pedestrian impact. If the stiffener is fixed it may be damaged if it strikes an obstacle in the vehicle's path.